Thread: stock size for m12

does anyone know what diameter is needed to cut an m12 thread. also is there a free chart with die sizes i have one for tapping but not for dies.

Are you talking about an internal m12 or an external m12 thread .
If your turning an external m12 thread you need 12mm stock

hmmmmmm I am going to take a stab in the dark and say 12mm

From wikipedia
A cylindrical blank, which is usually slightly less than the required diameter, is machined with a taper (chamfer) at the threaded end. This chamfer allows the die to ease onto the blank before it cuts a sufficient thread to pull itself along.[8]
The adjusting screws allow the die to be compressed or expanded to accommodate slight variations in size, due to material, manufacture, or die sharpness.


Russell

okay so when you're cutting external thread the stock needs to be the same size eg m6 6 mm and m8 is 8mm.

No, you need a bit of clearance. "A bit" will normally do, but if you want to be precise, the standard clearance for metric threads is .1082P. That is, pitch x .1082. Pitch for 12mm metric coarse is 1.75, so your clearance is 0.18935. Thats radial, so double it for diameter = 0.3787 and subtract that from nominal (12) = 11.6213mm.

I got this from the Engineers Black Book by Pat Rapp. Worth having.

Edit: The other replies are correct in that 12mm would be the best stock material size to start with, and your question did say stock.
Edit: Assuming you will turn it down to suit your needs.

I agree with Bryan, if you pick up any standard metric bolt and measure it, it will be under size.
The dies you buy are mostly for cleaning threads, and if you try to cut a M12 thread with a die on a piece of 12mm bar it will tear and not want to thread onto it, because it's to big.

Dave

If you wanted to turn the thread the max dia would be 11.966mm and min dia would be 11.701mm for a class 6g .

Here's a list of metric internal and external threads dimensions.